David Cameron was forced to explain on Friday why No 10 ignored a warning before the general election that his communications chief, Andy Coulson, had employed a freelance private detective with a long track record of corruption who was at the time facing a murder charge.

The Guardian disclosed that it had passed to a senior Cameron aide information about the News of the World's links to the detective, Jonathan Rees, which could not at the time be reported because Rees was awaiting trial for an axe murder.